Yes, of course, you can unsubscribe anytime you want! If you unsubscribe not later than 24 hours before your Free Trial expires, you won't be charged. If you unsubscribe anytime later, you won't be charged any further after your cancelation date. You can subscribe and unsubscribe as many times as you want.
If you'd like to cancel your subscription please follow these steps:
In Android StretchIt version 3.0.20 and up, please tap Home in the Main Menu, then your Profile Picture on the top left corner, then Subscriptions and Manage in Play Market.
In Android StretchIt version 2.5.7 and below, please tap My Profile in the Main Menu, then Settings on the top right corner, then Manage Subscriptions and Manage Subscriptions in Play Market.
You will still have access to the classes till the end of your trial period or the month (or year) you paid for.